A screen display's mixed signals

Updated 7:20 am, Thursday, September 13, 2012

Mariana Figueiro, associate professor at RPI and director of the LRC's Light and Health program, tested the effects of self-luminous tablets on melatonin suppression at the college in Troy, NY Tuesday Sept. 11, 2012. (Michael P. Farrell/Times Union)

Mariana Figueiro, associate professor at RPI and director of the...

Mariana Figueiro, associate professor at RPI and director of the LRC's Light and Health program, tested the effects of self-luminous tablets on melatonin suppression at the college in Troy, NY Tuesday Sept. 11, 2012. (Michael P. Farrell/Times Union)

Mariana Figueiro, associate professor at RPI and director of the...

Mariana Figueiro, associate professor at RPI and director of the LRC's Light and Health program, tested the effects of self-luminous tablets on melatonin suppression at the college in Troy, NY Tuesday Sept. 11, 2012. (Michael P. Farrell/Times Union)

Mariana Figueiro, associate professor at RPI and director of the...

Mariana Figueiro, associate professor at RPI and director of the LRC's Light and Health program, tested the effects of self-luminous tablets on melatonin suppression at the college in Troy, NY Tuesday Sept. 11, 2012. (Michael P. Farrell/Times Union)

Mariana Figueiro, associate professor at RPI and director of the...

Graduate assistant Brittany Wood worked with Mariana Figueiro, associate professor at RPI and director of the LRC's Light and Health program, as they tested the effects of self-luminous tablets on melatonin suppression at the college in Troy, NY Tuesday Sept. 11, 2012. (Michael P. Farrell/Times Union)

Graduate assistant Brittany Wood worked with Mariana Figueiro,...

Mariana Figueiro, associate professor at RPI and director of the LRC's Light and Health program, tested the effects of self-luminous tablets on melatonin suppression at the college in Troy, NY Tuesday Sept. 11, 2012. (Michael P. Farrell/Times Union)

Two hours in front of a backlit screen of a tablet computer is enough to significantly suppress melatonin production, said Mariana Figueiro, associate RPI professor and director of the center's Light and Health Program. Melatonin diminishment can in turn push back the time when a person will eventually fall asleep.

Low-frequency light from a screen that enters the eye essentially signals the human body that it is still daylight, and thus not time for melatonin production to promote sleep. On the other hand, dimming light signals the body that night has fallen, and that sleep should follow.

In addition to sleep disruption, chronic decreased melatonin levels have also been linked to increased risk of obesity and certain illnesses, including cancer and diabetes, in people who work night shifts for prolonged periods.

People who have invested in big-screen televisions don't have to worry about disrupting their melatonin, said Figueiro. While those screens emit lots of light, people normally sit so far away while watching that much less low-frequency light reaches the eye, previous research has found.

Tablets and larger computers, by comparison, are used more closely, and it is that proximity that is responsible for the effect.

Recently published in the journal Applied Ergonomics, the study examined 13 young people who were put before iPad, iPad 2 or PC tablet computer screens for one or two hours between 11 p.m. and 1 a.m. on Friday nights over a three-week period. An hour spent in front of a screen had little effect on melatonin levels, but spending two hours resulted in an average melatonin decrease of 22 percent, the study found.

Co-authors of the study are center Director Mark Rea, center research specialist Brittany Wood, an East Greenbush resident who used the project for her master's thesis, and center research nurse Barbara Plitnick.

Said Wood, "These electronic devices emit light at short wavelengths, which makes them potential sources for suppressing or delaying the onset of melatonin in the evening, reducing sleep duration and disrupting sleep. This is particularly worrisome in populations such as young adults and adolescents, who already tend to be night owls."

Melatonin production is part of a chain of events that starts in the eye. Light stimulates a nerve pathway from the eye's retina to a part of the brain called the hypothalamus. There, signals are sent that control hormones, body temperature and other functions that play a role in making people feel sleepy or awake.

Light hitting the retina causes the brain to perform certain tasks, such as raising body temperature and releasing stimulating hormones like cortisol, while suppressing melatonin.

Melatonin is made in the pineal gland, a pea-size gland in the brain. Normally, the pineal gland is activated about 9 p.m. each night to begin releasing melatonin. Levels remain elevated for about 12 hours before dropping again.

Figuerio said she does not advise people who want stay up late on the computer night after night to simply start popping over-the-counter melatonin pills to get their sleep.

Rather, she said, the research also found that using colored filters on light that reaches the eyes can make a difference. Blue filters actually strengthen low-frequency light that reaches the retina, thus suppressing melatonin production.

Figuerio said such colored filters can be obtained through theatrical supply shops, and can be wrapped around computer screens to negate the melatonin suppression effect.

Or, people can limit their computer use later in the evening, she said.

The use of light to manipulate melatonin levels is already being applied in agriculture, where extended periods of light are used to induce cows and chickens to produce more milk and eggs. Light therapy is also being used for patients with Alzheimer's disease to induce more regular sleep patterns.